1. Field of the Invention
The invention relates to a circuit configuration for routine testing of the clock supply of a large number of units operated with the same clock, preferably units of a digital time division multiplex telecommunication system, in which two clock generators are synchronized with respect to frequency but are not phase-locked, and depend on the switching position of a switching device supply as an active clock generator. A doubled distribution system, is provided having two parts to which the individual units are optionally connected and in which the common time for the units or stand-by as a locked clock generator to take over the clock supply in the event a spare line is switched in. Each of the units has a monitoring device which responds when their individual clock supply fails.
2. Description of the Prior Art
In redundant clock supply routine testing, it is of particular importance that ensurance is given that in the event of replacement switching the clock generator which functioned up to this point as a stand-by generator as well as the supply paths to the distribution systems function properly. Due to the importance which is placed on clock supply in a central device, for example, of a telecommunication system, it is also desirable to check the operatability of the monitoring circuits themselves.
If it is not possible to synchronize the two clock generators phase-locked, each time change-over switching from the active clock generator to the stand-by clock generator takes place, then data disturbances occur which in the event of a switch over due to malfunction can be accepted since due to finite error recognition, time clock interruption is unavoidable. Change-overs in the course of routine tests done with relatively great frequency must be avoided.